Device For Insertion, Guidance And Evacuation Of Cylindrical Parts Such As Nuclear Fuel Pellets, In A Centreless Grinder

ABSTRACT

The invention relates to a device ( 1 ) for the insertion, guidance and evacuation of cylindrical parts to be ground in a centreless grinder ( 10 ). 
     According to the invention, micrometric means ( 4, 40, 41 ) for adjustment of the alignment of the guides at the entry ( 3 ) to and the exit ( 5 ) from the guide chute ( 2 ) are provided and these micrometric adjustment means are independent from each other. 
     The invention enables very precise adjustment of the alignment and prevents any shift of the parts.

TECHNICAL FIELD

The invention relates to a device for the insertion, guidance andevacuation of cylindrical parts such as nuclear fuel pellets in acentreless grinder.

It is particularly aimed at improving the reliability of centrelessgrinding.

The main application is grinding of nuclear fuel pellets for whichquality is strict and imposes requirements to avoid generating defectson the pellets.

PRIOR ART

Centreless grinding is a known advantageous grinding process forgrinding cylindrical parts, particularly for nuclear fuel pellets.

A centreless grinder usually includes two grinding wheels, one of whichis a drive wheel used to rotate the pellets on themselves and makingthem advance on a guide rail called the guide chute in the case ofnuclear fuel pellets, and the other is a grinding wheel with thefunction of grinding the pellet diameters by abrasion.

Obviously, the quality of ground nuclear fuel pellets depends on theefficiency of the centreless grinder itself, but also on the quality ofthe pellet transfer immediately on the entry side into the centrelessgrinder, in it, and immediately on the exit side from it, in other wordsthe quality of insertion of pellets into the guide chute, of theirguidance in the guide chute between the grinding wheel and the drivewheel and of their evacuation from the drive wheel when they have beenground.

The general purpose of the invention is to propose a solution to furtherimprove the transfer quality of cylindrical parts such as nuclear fuelpellets, immediately on the entry side into a centreless grinder, in itand immediately on its exit side.

One particular purpose is to propose a solution that is easy to use in aglove box environment.

PRESENTATION OF THE INVENTION

To achieve this, the purpose of the invention is a device for theinsertion, guidance and evacuation of cylindrical parts such as nuclearfuel pellets, in a centreless grinder comprising:

an insertion guide chute adapted to guide said cylindrical parts overthe length of the grinding wheel and drive wheel of a centrelessgrinder,

a first guide called the entry guide arranged at one longitudinal end ofthe guide chute and adapted to allow the insertion of cylindrical partsone by one onto the guide chute from a conveyor system on the entry sideof the centreless grinder,

mechanical means for adjustment of the entry guide relative to the guidechute,

a second guide called the exit guide arranged at the other longitudinalend of the guide chute and adapted to transfer parts from the chute to aconveyor system on the exit side from the centreless grinder,

mechanical means for adjustment of the alignment of the exit guiderelative to the guide chute.

According to the invention, mechanical means for the micrometricadjustment of the alignment of the entry guide are independent from thealignment means of the exit guide.

In other words according to the invention, means of adjusting thealignment of the entry and exit guides are provided that enable a veryprecise alignment of the guides and the space between the grinding anddrive wheels, to within the nearest micrometre. Making the twoadjustment means independent enables an even more precise adjustment.This prevents any shifting of the parts to be ground such as nuclearfuel pellets, still present between the grinding wheels.

Thus, the parts (fuel pellets) may be inserted at the entry to thecentreless grinder with no mechanical interference between them.

Similarly, there is a continuity in the contact line of the ground partsand the drive wheel at the exit from the grinder. This prevents grindingdefects related to discontinuity in the contact as is possible in thestate of the art.

Preferably, the guide chute is a single piece steel part on whichsurface and in-core annealing and quenching heat treatments have beenmade. These treatments may preferably be completed by surface treatmentsonce the part (guide chute) has been finished, to increase somecharacteristics such as a better coefficient of friction and greaterresistance to wear. This steel is preferably an XC 38 steel.

Guide chutes according to the state of the art for a centreless grinderapplication for nuclear fuel pellets are composed of a steel base onwhich a tungsten carbide plate has been added that forms the actualguide rail for the pellets, in other words the part in direct contactwith the pellets to be ground.

The advantage of a tungsten carbide plate is that it has a very goodresistance to wear. The major disadvantage is its brittleness undershocks and internal stresses in the steel base. Thus, the disadvantagesof guide chutes according to the state of the art are avoided by makinga single-piece steel chute with in-core and surface heat treatmentsproviding wear resistance equivalent to tungsten carbide and goodresistance to shocks and the relaxation of internal stresses in thechute.

According to one advantageous embodiment, at least one of the two guidesis composed of two strips, one of which is fixed and parallel to thelongitudinal edge of the chute placed on the grinding wheel side and theother is installed on a pivot that adjusts the space from the fixedguide facing it, the distance from the pivoting guide being varied byactuation of mechanical means for adjusting the alignment of said guide.Preferably, the entry guide and the exit guide are each composed of twostrips, one of which is fixed and parallel to a longitudinal edge of thechute and the other is free to pivot to adjust the spacing of the guidefrom the fixed guide facing it.

Also preferably, the axis of the pivots of the adjustable guides isfitted with a polymer bearing. This makes the pivot axis compatible withthe dust and splinters from pellets during grinding, and consequentlyeliminates the risk of seizure.

According to one advantageous variant embodiment:

the pivot axis of the pivoting strip of the entry guide and/or the exitguide is (are) mounted in a support,

the mechanical micrometric means for adjustment of the alignment of theentry guide relative to the guide chute and/or the mechanical adjustmentmeans of the exit guide comprise a first screw screwed into the pivotaxis support and a second screw nested into the first screw with asmaller pitch than the first screw and adapted to bear in contact with apart of the pivoting strip, screwing of the first screw into the supportcausing translation of the two screws while screwing the second screwinto the first screw and bearing in contact with the part of thepivoting strip causes pivoting of the pivoting strip.

The pitch of the second screw is smaller than but sufficiently close tothe pitch of the first screw to create a micrometric adjustment of thepivoting strips, so as to obtain the greatest possible precision. Thedevice advantageously comprises a spring adapted to compensate forfunctional clearances of the device by guaranteeing permanent bearingbetween the second screw and the pivoting strip.

Each pivot axis and screw axis support is fixed to the guide chute, tofacilitate assembly.

Each pivot axis and screw axis support is shaped in a turret with thetwo screws nested in each other and arranged in the upper part of theturret.

Due to a turret type arrangement, the alignment adjustments can be mademanually by manipulating the screws from the top. This is perfectlysuitable for a glove box environment in which the centreless grinder isinstalled.

The geometric shape and the length of the exit guide are preferablyadapted to limit the number of ground cylindrical parts buffered at theexit from the wheels. In other words, this avoids the accumulation ofpellets, some of which could collect between the grinding wheels and bemachined beyond the required tolerances. The inclination of the exitguide and the inclined length cause the evacuation of the pellets whilelimiting their kinetic energy during evacuation to the conveyor on theexit side so that they remain in the horizontal position on theconveyor.

If their kinetic energy were not limited, they would be likely to tip onthe conveyor which could damage their final quality.

The device preferably forms a single piece assembly to which adaptedhandles are fixed to enable its insertion into and evacuation from acentreless grinder in a glove box. Making it easy to remove the devicemanually facilitates maintenance operations on the centreless grinder.

The invention also relates to a centreless grinder comprising a devicedescribed above. Such a centreless grinder is adapted to grinding ofnuclear fuel pellets.

Finally, the invention relates to a glove box in which a centrelessgrinder is arranged as above.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and characteristics will become clear after reading thedetailed description given below with reference to the following figuresamong which:

FIG. 1 is a perspective view of the side of the entry guide of a deviceaccording to the invention in a non-installed configuration,

FIG. 2 is another perspective view of a device according to theinvention in a non-installed configuration but on the exit guide side,

FIG. 3 is a side view of a device according to the invention in itsconfiguration installed in a centreless grinder for nuclear fuelpellets,

FIGS. 3A and 3B are cross-sectional views on lines A-A and B-Brespectively of the device according to FIG. 3.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

The terms “lower”, “upper”, “below”, “above”, “entry side” and “exitside” should be considered in the installed configuration of device 1according to the invention, in other words with the guide chute in thehorizontal position between the grinding wheel and the drive wheel of acentreless grinder as shown in FIG. 3.

The device 1 according to the invention includes firstly a guide chute 2adapted to guide pellets over the length of the grinding wheel 8 anddrive wheel (not shown) of a centreless grinder 10 shown in FIG. 3.

The guide chute 2 is a single piece part made of XC 38 steel on whichsurface and in-core quenching and annealing heat treatments have beenperformed. The heat treatments were done to give the guide chute wearresistance equivalent to tungsten carbide, good shock resistance and sothat the chute 2 has no internal stresses. This chute 2 comprises anupper part 20, the function of which is to guide the pellets P ofnuclear fuel. As can be better seen in FIGS. 3A and 3B, the guide part20 is inclined and is delimited by two longitudinal edges 200, 201.

An entry guide 3 is arranged at a longitudinal end of the guide chute 2:it is adapted to enable pellets P to be slid onto the chute 2 from aconveyor system not shown on the entry side of the centreless grinder10. This entry guide 3 comprises a fixed strip 30 approximately alignedon the longitudinal edge 200 of the chute 2 and another strip 31 free topivot to change the inclination relative to the other longitudinal edge201 of the chute 2.

The strip 31 is installed free to pivot on an axis 310 fitted with apolymer bearing installed in a support 32 arranged as a turret.

The alignment of the pivoting strip 31 is adjusted relative to the edge201 of the chute by mechanical means 4. These means are composed of twoscrews 40, 41, one nested into the other in the upper part of the turret32 (FIG. 3A). The first screw 40 is screwed into the support 32. Thesecond screw 41 has a smaller pitch which is similar to the pitch of thescrew 40, and the screw 41 is fixed in rotation.

Rotating the screw 40 causes translation along its axis relative to thefixed support 32 (screw-nut connection). At the same time, this rotationof the screw 61 creates a second translation along its axis relative tothe second screw 41. The difference in pitch results in a smalltranslation of the bearing point of the screw 41 on the guide 31, whichrotates the guide 31. Such adjusting means 4, 40, 41 make it possible toachieve very precise adjustment of the alignment of the pivoting strip31, to the nearest micrometer.

A spring 42 compensates for functional clearances of the device toachieve permanent bearing between the screw 41 and the strip 31 in thepivoted position.

Due to the shape and dimensional characteristics of the entry guide 5and the alignment adjustments of the pivoting strip described above, thenuclear fuel pellets P can be inserted with no mechanical interferencebetween them.

An exit guide 5 is arranged at the other longitudinal end of the guidechute 2; it is adapted to enable transfer of pellets P from the chute 2to a conveyor system not shown at the exit from the centreless grinder10.

The assembly and arrangement of the entry guide 5 with the means ofadjusting the alignment of the pivoting strip 31 are made in a similarmanner for the exit guide 5, the adjustment means 6, 60, 61 of thepivoting strip 51 of the exit guide 5 being independent of theadjustment means 4, 40, 41 of the pivoting strips 31 of the entry guide3.

Thus, the exit guide 5 comprises a fixed strip 50 approximately in linewith the longitudinal edge 200 of the chute 2 and another strip 51installed free to pivot to change the inclination relative to the otherlongitudinal edge 201 of the chute 2.

The strip 51 is installed free to pivot on an axis 510 provided with apolymer bearing installed in a support 52 arranged as a turret.

Mechanical means 6 are provided to adjust the alignment of the pivotingstrip 51 relative to the edge 201 of the chute. These means are composedof two screws 60, 61 nested in each other in the upper part of theturret 52 (FIG. 3B). The first screw 60 is screwed into the support 52.The second screw 61 has a smaller pitch but similar to the pitch of thescrew 60 and the screw 61 is fixed in rotation. Rotation of the screw 60causes translation along its axis relative to the fixed support 52(screw-nut connection). At the same time, this rotation of the screw 60causes a second translation along its axis relative to the second screw61. The difference in pitch results in a small translation of thebearing point of the screw 61 on the guide 51 which causes a rotation ofthe guide 51. Such adjustment means 6, 60, 61 are capable of achievingvery precise adjustment of the alignment of the pivoting strip 51 to thenearest micrometer.

A spring 62 for compensation of functional clearances of the device isinstalled between the pivoting strip 51 and the support 52; it can thusprovide a permanent bearing between the screw 61 and the strip 51 in thepivoted position.

As shown, the geometric shape and length of the outlet guide 5 areadapted to limit the number of ground pellets in the buffer and theirexit speed. This prevents said pellets P from tipping on the conveyorsystem at the exit from the centreless grinder 10.

As shown in FIGS. 1 and 2, the device 1 according to the invention 1forms a single piece assembly to which pivoting handles 70, 71 arefixed, adapted to enable the insertion into and withdrawal from acentreless grinder 10. This facilitates maintenance operations that aredifficult in a glove box environment.

The assembly 1 is single piece because:

-   -   the turrets 32, 52 in which the pivoting strips 31, 51 are        installed with adjustment means 4, 6 and    -   the supports 72 of handles 70, 71 to which the fixed strips 30,        50 are fixed, are fixed by screwing to the guide chute which is        itself a single piece.

Although described as a reference to an application in a centrelessgrinder in which the functions of the device are insertion, guidance andevacuation of nuclear fuel pellets in a centreless grinder, anyapplication that requires insertion, guidance and evacuation ofcylindrical parts with very high precision to prevent any shift of theparts, could also be envisaged.

1. Device for the insertion, guidance and evacuation of cylindricalparts such as nuclear fuel pellets, in a centreless grinder, comprising:an insertion guide chute adapted to guide said cylindrical parts overthe length of the grinding wheel and drive wheel of a centrelessgrinder, a first guide, called the entry guide, arranged at onelongitudinal end of the guide chute and adapted to allow the insertionof cylindrical parts one by one onto the guide chute from a conveyorsystem on the entry side of the centreless grinder, mechanical means formicrometric adjustment of the entry guide relative to the guide chute, asecond guide, called the exit guide, arranged at the other longitudinalend of the guide chute and adapted to transfer parts from the chute to aconveyor system on the exit side from the centreless grinder, mechanicalmeans for micrometric adjustment of the alignment of the exit guiderelative to the guide chute, wherein the mechanical means formicrometric adjustment of the alignment of the entry guide areindependent from the micrometric alignment means of the exit guide. 2.Device according to claim 1, in which the guide chute is a single piecepart made of XC 38 steel, on which surface and in-core annealing andquenching heat treatments have been made and preferably surfacetreatments once the guide chute has been finished.
 3. Device accordingto claim 1, in which at least one of the two guides is composed of twostrips one of which is fixed and parallel to the longitudinal edge ofthe chute and the other is installed on a pivot that adjusts the spacefrom the fixed guide facing it, the distance from the pivoting guidebeing varied by actuation of mechanical means for adjusting thealignment of said guide.
 4. Device according to claim 3, in which theentry guide and the exit guide are each composed of two strips, one ofwhich is fixed and parallel to a longitudinal edge of the chute and theother is free to pivot to adjust the spacing of the guide from the fixedguide facing it.
 5. Device according to claim 3, in which the pivotingstrip of the two guides is installed pivoting about an axis fitted witha polymer bearing.
 6. Device according to claim 4, in which: the pivotaxis of the pivoting strip of the entry guide and/or the exit guide is(are) mounted in a support, the mechanical micrometric means foradjustment of the alignment of the entry guide relative to the guidechute and/or the mechanical adjustment means of the exit guide comprisea first screw screwed into the pivot axis support and a second screwnested into the first screw, with a smaller pitch than the first screwand adapted to bear in contact with a part of the pivoting strip,screwing of the first screw into the support causing translation of thetwo screws while screwing the second screw into the first screw andbearing in contact with the part of the pivoting strip causes pivotingof the pivoting strip.
 7. Device according to claim 6, in which thepitch of the second screw is smaller than but sufficiently close to thepitch of the first screw to create a micrometric adjustment of thepivoting strips.
 8. Device according to claim 6, comprising a springadapted to compensate for functional clearances of the device byguaranteeing permanent bearing between the second screw and the pivotingstrip.
 9. Device according to claim 7, in which each pivot axis andscrew axis support is fixed to the guide chute.
 10. Device according toclaim 7, in which each pivot axis and screw axis support is shaped in aturret with the two screws nested in each other and arranged in theupper part of the turret.
 11. Device according to claim 1, in which thegeometric shape and the length of the exit guide are adapted to limitthe number of ground cylindrical parts buffered at the exit from thewheels.
 12. Device according to claim 1, forming a single piece assemblyto which adapted handles are fixed to enable its insertion into andremoval from a centreless grinder.
 13. Centreless grinder comprising: aninsertion guide chute adapted to guide said cylindrical parts over thelength of the grinding wheel and drive wheel of a centreless grinder, afirst guide, called the entry guide, arranged at one longitudinal end ofthe guide chute and adapted to allow the insertion of cylindrical partsone by one onto the guide chute from a conveyor system on the entry sideof the centreless grinder, mechanical means for micrometric adjustmentof the entry guide relative to the guide chute, a second guide, calledthe exit guide, arranged at the other longitudinal end of the guidechute and adapted to transfer parts from the chute to a conveyor systemon the exit side from the centreless grinder, mechanical means formicrometric adjustment of the alignment of the exit guide relative tothe guide chute, wherein the mechanical means for micrometric adjustmentof the alignment of the entry guide are independent from the micrometricalignment means of the exit guide.
 14. Centreless grinder according toclaim 13, adapted to grinding of nuclear fuel pellets (P).
 15. Glove boxin which a centreless grinder is arranged according to claim
 13. 16.Device for the insertion, guidance and evacuation of cylindrical partssuch as nuclear fuel pellets, in a centreless grinder, comprising: aninsertion guide chute adapted to guide said cylindrical parts over thelength of the grinding wheel and drive wheel of a centreless grinder, afirst guide, called the entry guide, arranged at one longitudinal end ofthe guide chute and adapted to allow the insertion of cylindrical partsone by one onto the guide chute from a conveyor system on the entry sideof the centreless grinder, a first plurality of screws for micrometricadjustment of the entry guide relative to the guide chute, a secondguide, called the exit guide, arranged at the other longitudinal end ofthe guide chute and adapted to transfer parts from the chute to aconveyor system on the exit side from the centreless grinder, a secondplurality of screws for micrometric adjustment of the alignment of theexit guide relative to the guide chute, wherein the first plurality ofscrews for micrometric adjustment of the alignment of the entry guideare independent from the second plurality of screws for micrometricalignment means of the exit guide.
 17. Device according to claim 15, inwhich the first plurality of screws and/or the second plurality ofscrews comprise a first screw and a second screw nested into the firstscrew.